A common hydrometer reads specific gravity of liquids. Compared to the mark 1.6 on the stem, the mark 1.5 will be:

A hydrometer is an instrument that is used to determine specific gravity.Hydrometer operates on the Archimedes principle which states that a solid body displaces its own weight within a liquid in which it floats.Lesser the specific gravity of any liquid, lighter the liquid will be with respect to water, the deeper the hydrometer will sink. This is because, the greater amount of liquid will be requested to equal the weight of the body.Hence, 1.5 mark will be above 1.6 mark.